Cat owners often write in a particularly annoying way. I don't need to know that Sir Fluffington Tabbyworth rises at 5am to deign to request that his slaves furnish him with a biscuit. I just asked what time you get up.
Anyone can cheat. Posters insisting they just know their husband would never cheat are wrong, not in the sense that he necessarily will (I'm sure most of them won't!), but because unless you knowingly shack up with a big shagger, no-one expects their partner will cheat on them.
If the OW/OM knew the affair partner was in a relationship, then they're also culpable for the hurt and anger caused. Yes, 'they didn't make any vows to you', but there are lots of things we don't make any vows to people about and still don't go about doing. The pious whinging at devastated posters who've discovered their husband was having an affair over being vitriolic towards the OW is just virtue signalling. Of course it's easier to be, in the short term, more viscerally angry towards someone who you don't have to unpick your life apart from, who you don't share a history with.
Childfree/destination weddings are fine so long as the b&g accept that some people may not be able to make it as a result. People insisting their kids be invited because they remember having fun 'sliding around on the floor' (always the sliding) at weddings as a child are invariably the sort who would sit beaming while their child yelled throughout the vows.
Envy is a totally normal emotion, in the same way happiness and anger are.